A calcium-activated protease which specifically degrades neurofilaments has been studies. The characteristics of this protease indicate that it may be involved in fomration of nerve terminals during development. Co-valent labeling techniques developed in our laboratory suggest that there is a slow retrograde transport wave in mammalian nerves which contains serum albumin. Analysis of neurosecretory vesicle membrane proteins have led to the finding of two monoclonal antibodies which react specifically with two membrane proteins. Using monoclonal antibodies against H-2 and Thy-1 antigens in immunocytochemical experiments on mouse brain shows that selective brain cells contain these antigenic determinants.